1. Field of the Invention
The present invention relates to a planographic printing plate precursor which can record an image by laser and can be on-press developed, and a printing method using the same.
2. Technical Field
Generally, a planographic printing plate has a configuration having at least a lipophilic image portion for receiving ink in the printing process and a hydrophilic non-image portion for receiving dampening water. Planographic printing is a printing method such that a lipophilic image portion and a hydrophilic non-image portion in a planographic printing plate are used as an ink receiving portion and a dampening water receiving portion (an ink non-receiving portion) respectively by utilizing a property of repulsion of water and oil-based ink with each other, and a difference in adherability of ink is caused on the surface of the planographic printing plate to impress ink on only the image portion and thereafter transfer the ink to an object to be printed such as paper.
Conventionally, a planographic printing plate precursor (PS plate) provided with a lipophilic photosensitive resin layer (an image recording layer) on a hydrophilic support has been widely used in order to produce this planographic printing plate. Ordinarily, a planographic printing plate is obtained by performing plate-making by a method such that a planographic printing plate precursor is exposed to an original image such as a lith film, and thereafter an image recording layer corresponding to an image portion is made to survive, and an unnecessary image recording layer corresponding to a non-image portion is dissolved and removed by alkaline developing solution or organic solvent-containing developing solution, and a hydrophilic support surface is exposed to form a non-image portion.
When making a printing plate from a conventional planographic printing plate precursor, it is necessary to remove undesired portions of the image recording layer through dissolution in a developer or the like after exposure. There has recently been a demand for elimination or simplification of such an additional wet processing. In particular, in recent years, the disposal of waste fluid discharged with wet processing has been a great concern in the whole industrial world in consideration of the terrestrial environment, so that a request to solve the problem has been increasingly strengthened.
Under the circumstance, a so-called on-press development method has been proposed as a simplified platemaking method. In the on-press development method, an image recording layer allowing removal of undesired portions of the image recording layer of the planographic printing plate precursor in the normal printing step is used, and the undesirable portions of image recording layer are removed on-press after exposure.
Specific examples of the on-press development include a method for using a planographic printing plate precursor having an image recording layer capable of being dissolved or dispersed in dampening water, ink solvent or emulsion of dampening water and ink, a method for dynamically removing an image recording layer by contact with rollers and blanket of a printing press, and a method for weakening cohesive force of an image recording layer or adhesive force of an image recording layer and a support by penetration of dampening water and ink solvent to thereafter dynamically remove the image recording layer by contact with rollers and blanket.
In the invention, unless otherwise described, “developing” and “development (process)” mean using an apparatus (typically, an automatic developing machine) other than a printing press to contact an image recording layer with a liquid (typically, alkaline developing solution) so that the image recording layer in an unexposed portion in a planographic printing plate precursor is removed to expose a hydrophilic support surface. The “on-press developing” and “on-press development” mean a method and a process to use a printing press to contact a image recording layer with a liquid (typically, printing ink and/or dampening water) so that the image recording layer in an unexposed portion in a planographic printing plate precursor is removed to expose a hydrophilic support surface.
Digitalization technology of processing, storing, and outputting image information electronically in and out of computer has been widely spreading recently as an image forming means on the planographic printing plate precursor, and various new image-outputting systems compatible with the digitalization technology have been put into practical use. Computer to plate (CTP) technology of producing a planographic printing plate directly without use of a lith film by making a highly converged radiation ray such as laser radiation carry such digitalized image information and scan-irradiating the planographic printing plate precursor with the ray is attracting attention in the above situation. Accordingly, it is one of important technical issues to obtain a planographic printing plate precursor suitable for such technology.
In the simplification, the drying or the process-freeing of plate-making work as described above, an image recording layer after being exposed is not fixed through the development process, thus the image recording layer after being exposed has photosensitivity to bring a possibility of causing fog before printing. Therefore, an image recording layer and a light source capable of being handled in a bright room or under a yellow light are needed.
With regard to such a laser light source, a solid-state laser such as a semiconductor laser or a YAG laser for radiating infrared rays with a wavelength of 760 to 1200 nm is extremely useful for the reason that a high-output and small-sized solid-state laser is available inexpensively. An UV laser may be also used.
Examples of a planographic printing plate precursor subjected to the on-press development for recording an image by this infrared laser include a planographic printing plate precursor having an image recording layer, in which hydrophobic thermoplastic polymer particles are dispersed in a hydrophilic binder, on a hydrophilic support is described in Japanese Patent No. 2938397. It is described in Japanese Patent No. 2938397 that the planographic printing plate precursor is exposed to an infrared laser, and the hydrophobic thermoplastic polymer particles are integrated by heat to form an image, and thereafter the planographic printing plate precursor is mounted on a cylinder of a printing press to be capable of performing the on-press development by dampening water and/or ink.
The method for forming an image with integration of fine particles by mere heat seal in this manner has a problem that image intensity is extremely weak and printing durability is insufficient even though favorable on-press developability is exhibited.
Also, a planographic printing plate precursor having a microcapsule including a polymerizable compound on a hydrophilic support is described in Japanese Patent Application Laid-Open (JP-A) Nos. 2001-277740 and 2001-277742.
Further, a planographic printing plate precursor having a photosensitive layer containing an infrared absorbing agent, a radical polymerization initiator and a polymerizable compound on a support is described in JP-A Nos. 2002-287334 and 2005-329708+A planographic printing plate precursor having a photosensitive layer containing a polymer compound which contains at least one ethylenically unsaturated bond is also described therein. The methods using polymerization reaction in this manner are so high in chemical bonding density of an image portion as compared with an image portion formed by heat seal of polymer fine particles that image intensity is comparatively favorable and favorable printing durability may be exhibited. However, the methods using polymerization reaction are still insufficient in view of on-press developability. Specifically, the problem in the deterioration in the on-press developability after lapse of days is remarkable.
For improving on-press developability, there is a method of using a polymer compound including at least one of an ether group, an ester group and an amido group, as described in JP-A No. 2006-116941. However, this method has a problem of insufficient printing durability.
Improvements in both of removability of unexposed portions (non-image regions) upon development, and in printing durability have also been desired for planographic printing plate precursors to be subjected to development treatment.